In inkjet recorders of the type disclosed in this patent application, a pair of rows of orifices receive an electrically conductive recording fluid from a pressurized fluid manifold, and eject the fluid or ink in two rows of streams. The fluid flows through the orifices in a nozzle plate, with the formation or breakoff of the fluid stream into discrete drops being stimulated by the application of a series of traverse waves to the fluid cavity.
Graphic reproduction in recorders of this type is accomplished by selectively charging and deflecting some drops in each of the streams and thereafter, depositing these charged drops in a moving web of paper or other material, with the uncharged drop continuing on an undeflected path and being captured in ink return gutters. The direction of web movement is substantially perpendicular to the rows or orifices in most such systems, such as shown in U.S. Pat. No. 3,701,998. Charging of the drops in such systems is accomplished by application of charge control signals to charging electrodes near the edge of each individual drop stream. As the drops separate from their parent fluid filaments, they carry a portion of the charge applied to the charging electodes. Thereafter, the drops pass through electrostatic fields which have no effect on the uncharged drops, but which cause the charged drops to be deflected in an amount proportional to the strength of the field and the charge carried by the drop.
One problem with printers of this type and with all types of inkjet printers has been attaining sufficient image resolution. Since a discrete number of drops are applied to form the images, it is clear that image definition may be improved by increasing the number of drops, and by providing a proportionate increase in data handling capability. If, however, only one print position per line is serviced by each orifice, the number of drops per unit width, and therefore, the resolution of an image in the direction transverse to the web is limited by the minimum dimensions required for each orifice. The approach taken in the above cited '998 patent is to provide two rows of drop streams which are staggered. The charging of drops in the two rows is timed such that printing from the two rows of streams is in registration. The distance between adjacent streams in each of the rows is therefore twice the distance which would separate streams in a printer of comparable resolution having one row of streams.
In U.S. Pat. No. 4,085,409, an approach is described which is illustrated in FIG. 6 of the present application, specifically, nozzle 1 prints one block of dots along a row, while nozzle 2 prints an adjacent block of dots, the adjacent blocks being strung together to form a line. However, this results in large gaps in the printing if one nozzle fails, or in small gaps at the interface between adjacent blocks of drops due to the inevitable difference in the directionality of the jetstreams.
An effort to deal with this is also disclosed in U.S. Re. Pat. No. 28,219 wherein a printer has a plurality of separate orifice arrays positioned in tandem, with each successive array being laterally offset. The orifices are positioned such that they interlace to provide print capability across the entire web. The orifice arrays extend perpendicular to the direction of movement. In this system, accurate registration of drops is difficult because all the tolerances associated with: the fabrication and assembly of multiple arrays, the synchronization of droplets emanating from different arrays, and the speed variation of the recording medium.
An alternative approach is disclosed in U.S. Pat. No. 3,739,395, for example, wherein uncharged drops are caught and do not print while charged drops from each orifice are deflected by two sets of deflection electrodes to a plurality of discrete print positions on the moving web. In this way, deflection of the drops can be perpendicular or parallel to the direction of web movement. However, in such case, the distance between orifices must be greater than if each orifice is serviced only by a single print position because deflection electrodes must be positioned on all sides of each orifice.
U.S. Pat. No. 3,871,004 discloses a similar system wherein the drops may be deflected obliquely; like the '395 patent, electrode configuration is bulky, limiting inner orifice spacing.
With the continued development of inkjet printers, the use of inkjet color printers has become highly desirable. In inkjet color printers now in use, a plurality of colored inks, for example, cyan, magenta and yellow are ejected to paint a color image in the form of an ink dot pattern. These inkjet color printers have used a method in which an image with half-tones is represented by controlling the quantity of ink drops to be deposited on dot matrices provided one for each of the picture elements on the recording web, and an image with complex colors represented by mixing different colors of ink drops. However, in such known systems, accurate registration of the drop streams on the recording web has been extremely difficult to achieve. Moreover, typically such systems require multiple drop generators, multiple drop charge plates, and multiple deflection electrodes to achieve two separate and additive objectives: high resolution and color. Therefore, in such systems the problems described for the above-cited U.S. Pat. No. 28,219 are compounded.